Optimizing the Effectiveness of Directed Energy Weapons with Specialized Weather Support

Accurate characterization of the atmosphere is essential to maximizing the use of directed energy (DE) weapons. Developing, procuring, and sustaining such weapons has been and will continue to be difficult; therefore, it is imperative that they achieve optimum effect when employed. The atmosphere, a highly dynamic medium in which these systems must operate, can significantly impact their effectiveness, thus necessitating an understanding of this environment and a capability to predict it. DE systems, particularly high-energy lasers (HEL) employed at low altitudes, will exhibit significant variations in performance based on location, time of day, and time of year. Through the Air Force Weather Agency, the Air Force Weather (AFW) community provides centralized terrestrial and space weather support to the Joint Chiefs of Staff, Air Force, Army, unified commands, national intelligence community, and other agencies as directed.1 This article outlines some of the unique atmospheric influences on DE weapons and the ways that specialized weather support can enhance the mission capability and efficacy of those weapons.

Anticipating the changing nature of warfare is part of the responsibility that AFW shares with other parts of the Department of Defense (DOD) after the terrorist attacks of 11 September 2001. AFW cannot afford to wait for DE weapons events to happen and then react. According to the Quadrennial Defense Review Report of 2006, “new capabilities [are] needed by Combatant Commanders to confront asymmetric threats.”2 Not all of the “new capabilities” are the weapons themselves; much of the advancing technology in the DE weapons realm involves the transition of high-fidelity modeling and simulation competencies into mission-planning tools. These decision aids, coupled with timely and accurate environmental assessments, would enable the DE weaponeer to optimize an employment strategy. AFW’s ability to guide the employment of DE weapons in all environments—via accurate determination of how to exploit information on target-area weather conditions to best advantage—is essential to secure the battlespace of tomorrow. Identifying the optimum time of day, attack heading, and attack altitude for low-altitude employment of HELs serves as an example of such information exploitation.

Major Types of Directed Energy Weapons

This article addresses two types of DE systems: the HEL and the high-power microwave (HPM). Whereas HELs direct a beam of focused energy to a precise point on the target to damage or destroy it, HPMs do not physically destroy a target. Rather, they invade the electronics and disrupt the components, circuitry, and switches inside the device. Additionally, they can cause behavior-modifying sensations in living organisms. HPMs, which do not require the precise aiming necessary for HELs, can function as area weapons, depending on the frequency, field of view, range to the target, and selection of either a large or small footprint.3

These weapons complement each other, each having advantages and disadvantages. HPM weapons cannot focus on as small an area as can HEL weapons but have proven effective through clouds and fog since they experience about two orders of magnitude less extinction (i.e., loss of energy due to absorption and scattering) in those conditions than do HELs. HPMs generate high electric fields over the entire target, in sharp contrast to the intense energy delivered by a laser to a typically small and precisely selected target area.4Furthermore, they can affect enemy electrical systems regardless of whether those systems are on or off.5 For example, HPMs can stop air-, land-, or seaborne systems in their tracks. Additionally, HEL and HPM systems can engage multiple targets nearly instantaneously since they propagate at the speed of light.6 DE systems can have a “deep magazine,” which means that their ability to fire is limited only by their capacity to recharge and cool themselves.7 Because DE weapons only expend energy, the cost per shot represents the sole cost of powering the device. Electrically generated and free-electron lasers require nothing more than power sources, eliminating the need to transport, store, and load munitions, and minimizing the logistical footprint, compared to conventional weapons. The fact that the factory can directly resupply chemical lasers eliminates the need for long-term storage.8 HEL weapons provide almost surgical precision, greatly minimizing the potential for collateral damage.

Issues with the Atmosphere

In a vacuum, electromagnetic energy travels unattenuated, reaching its target with the theoretical maximum energy available; however, Earth’s atmosphere contains mitigating factors that affect the intensity of DE received at the target. These factors include linear and nonlinear processes in the atmosphere that can affect the propagation of DE systems or electromagnetic energy in general. Linear processes are those in which the DE beams do not modify the characteristics of the atmosphere—for example, scattering caused by molecules, aerosols, rain drops, or other particles. Nonlinear effects such as thermal blooming, a defocusing of the beam caused by heating of the beam path due to absorption, result from the presence and intensity of the DE beam itself.9 Both linear and nonlinear effects combine to reduce intensity at the target.

Because the atmosphere decays exponentially with height, its effects on HEL/HPM propagation vary most dramatically in the vertical. Thus, a definition of the atmosphere’s vertical structure is in order. For the purposes of this article, the atmosphere consists of the boundary layer; lower, middle, and upper atmospheres; high altitude (as defined by the Air Force); and space regions (fig. 1).10 The atmospheric zone where each DE system operates influences not only those systems’ capabilities but also their support requirements.

Critical to the success of military weapon systems is understanding the conditions in which they must operate. Atmospheric differences can affect DE systems in various ways, depending on whether the weapon operates over water or land within the boundary layer or in the upper atmosphere (fig. 1). For example, although a system may operate in the boundary layer, many different climates exist within this area (e.g., desert, tropical, woodland), not to mention variations associated with the four seasons. The varied DE systems under development or planned for military use must account for the environments in which they are designed to function.

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